Comparative approaches toward diamines containing spatially separated homobenzylic and benzylic nitrogen stereocenters

Several synthetic strategies to diamines 1–3 are described. The optimum approach via opening of aziridine afforded 1–3 in 29–60% yield over 3–5 steps. A study on formation of the benzylic stereocenter using Toste’s rhenium-catalyzed asymmetric reduction of phosphinyl ketimines was also evaluated and afforded 15 in 92% de.